Second problem:
After the update has completed, when rebooting right after the BIOS finished its job, the system failed to boot, indeed it failed to load GRUB the boot loader with the message:

Failed open \EFI\BOOT\grubx64.efi - Not Found
Failed to load image \EFI\BOOT\grubx64.efi: Not Found
start_image() returned Not Found

Solution:
- Get a bootable USB or CD of RHEL / CentOS 7.3.
- Select "Rescue a Redhat Linux Installation" when presented with the CD / USB options.
- Ensure you don't get any errors and that you got a message saying that your system has been mounted under /mnt/sysimage.# chroot /mnt/sysimage
# cd /boot
- …